Solid-state foaming of commercial purity titanium was achieved by hot-isost
atic pressing of titanium powders in the presence of argon, followed by exp
ansion of the resulting high-pressure argon bubbles at ambient pressure and
elevated temperature. The foaming step was performed under isothermal cond
itions or during thermal cycling around the alpha/beta allotropic temperatu
re of titanium. Such thermal cycling is known to induce transformation supe
rplasticity (TSP) in bulk titanium due to the complex superposition of inte
rnal transformation stresses and an external biasing stress; TSP was found
to be active during foaming, where the deviatoric biasing stress was provid
ed by the internal pore pressure. As compared to isothermal control experim
ents where foam expansion occurred by creep only, TSP foaming under thermal
cycling conditions led to significantly higher terminal porosity (41% as c
ompared to 27%). The foaming rates were also higher for the TSP case before
pore growth ceased. Additionally, foaming experiments were conducted under
an externally applied uniaxial tensile stress of 1 MPa. This procedure res
ulted in foaming kinetics and porosities similar to those achieved without
an external stress and, for the TSP case, led to high aspect ratio pores el
ongated in the direction of the applied external stress.